Reuse VST2 audio processing buffers on Wine side

Just like we made similar changes on the plugin side a few commits ago
to prevent allocations there.

src/wine-host/bridges/vst2.h

@@ -107,6 +107,13 @@ class Vst2Bridge : public HostBridge {
      */
     Configuration config;
 
+    /**
+     * The object we'll serialize the response into after the plugin has
+     * finished processing audio. We reuse this object to avoid reallocations
+     * since it contains pointers to heap data.
+     */
+    AudioBuffers process_response;
+
     /**
      * We'll store the last transport information obtained from the host as a
      * result of `audioMasterGetTime()` here so we can return a pointer to it if